The association between parasitic infection and malnutrition in preschool children in the city of São Paulo, was studied according to degree of malnutrition, age, and income. Associations were assessed by risk analysis. Higher risks of malnutrition were found in children above 24 months of age infected with Ascaris, Trichuris or with more than three different parasites. The presence of more than three parasites per child affected nutritional status independently of income level. It is suggested that more attention should be given to intensity and chronicity of intestinal parasitic infection.